1. Field of the Invention
The present invention pertains to aryl polyols prepared by oxyalkylating starter molecules containing phenolic hydroxyl groups, and to the aryl polyols obtained thereby.
2. Background Art
Oxyalkylation of hydroxyl-functional starter molecules to prepare hydroxyalkyl-terminated polyols, generally hydroxyalkyl-terminated polyether polyols, has been practiced for some time. The physicochemical properties of the polyols are tailored to the particular end use. In general, low viscosities, relatively low polydispersity, and relatively low color are required of these products. In order that the polyols may be provided cost effectively, the production process is preferably of short duration.
Preparation of phenolic-based polyols is more problematic than those prepared from starters bearing aliphatic hydroxyl groups. The decreased basicity of alkali metal phenoxides and related compounds lowers the oxyalkylation rate considerably. In addition to the slow oxyalkylation, phenolic starters exhibit a relatively long xe2x80x9cinduction timexe2x80x9d prior to attaining a reasonable oxyalkylation rate.
Moreover, unlike the oxyalkylation of starters such as ethylene glycol, trimethylolpropane, and the like, where a homogenous or substantially homogenous reaction mixture is obtained during alkylene oxide addition, alkylene oxides are poorly soluble in phenolic compounds and vice versa. Thus, oxyalkylation of phenolic starters must generally take place in solution. Aromatic solvents such as toluene or xylene are preferred. However, the addition of solvent lowers the reaction rate due to dilution effects, and also requires subsequent removal of solvent, adding to the already long processing time.
The requirement for low viscosity products has been thought to require that relatively low oxyalkylation temperatures should be used, i.e., in the range of 100xc2x0 C. to 125xc2x0 C., as are conventionally used with aliphatic glycol-based polyether polyols. Increasing the temperature generally broadens the molecular weight distribution considerably, and increases the color of the product as well.
It would be desirable to provide a process for the preparation of aryl polyols which is less time consuming, and therefore more cost-effective. It would be further desirable to lower the induction time exhibited by phenolic starters, and to minimize solvent recovery. It would be yet further desirable to provide lower viscosity polyols at a given hydroxyl content.
It has now been surprisingly discovered that significant improvements may be made in the preparation of aryl polyols by a staged temperature process wherein a first oxyalkylation is conducted at a relatively high temperature, and further oxyalkylation conducted at a lower temperature. Contrary to what would be expected, the viscosity and polydispersity of the product polyols remain substantially the same, and in some cases are lowered, while dramatically decreasing both the induction period and the overall reaction time. The products are useful for many purposes, and may be aminated by conventional amination procedures to produce aminated products.